"Vitamin A type activity" is found in species which possess properties effecting cell growth and differentiation. Naturally occurring compounds possessing such activity are retinol, retinal and retinoic acid. All are unacceptable for use in humans since they are toxic and some of them accumulate in the liver. Thus, much effort has been devoted to developing retinoids having high activity (which may therefore be administered in low doses and yet be effective) and relatively low, if any, side effects. "Vitamin A activity" can be determined by numerous tests; it has been shown that a good correlation exists between the Tracheal Organ Culture (TOC) screen, in which reversal of keratinization is determined, and "vitamin A activity".
The use of retinoic acid in the treatment of acne vulgaris is known. Clinical trials in Europe have also been reported in which the effect of retinoic acid on epithelial tumors was discussed.
Two retinoids are in current use as prescription drugs for the treatment of acne and psoriasis, namely Isoretinoin and Etretinate, and have the following structure: ##STR3##
It is the primary object of the present invention to provide a new group of retinoids which display "vitamin A type activity". This and other objects of the present invention will become more apparent from the discussion which follows.